DE 103 56 916 A1 discloses to generate a space ignition in a combustion chamber in an internal combustion engine in order to better ignite and combust a fuel air mixture of an introduced fuel.
In conventional engines an ignitable mixture is compressed in a cone shaped cylinder head and caused by a spark plug to react and oxidize. Thus, a chemical oxidation spreads cone shaped from an ignition location as a pressure and reaction front (laminar combustion gas phase). The pressure front moves faster than the reaction front and therefore reaches a cylinder edge first. The pressure front is reflected at the cylinder edge and runs towards the reaction front. When, both fronts meet the reaction can die down which degrades efficiency and causes pollutants.
Replacing the local ignition by a space ignition through microwaves mitigates this effect. Before. Ignition the mixture shall be excited over the entire volume as homogeneously as possible which requires absorption that is distributed over the combustion chamber. Thus, an absorption capability for microwaves described by a material parameter tan δ (t) and an associated penetration depth are important.
During compression a pressure and temperature dependent ionization of the mixture to be ignited is already being performed. Due to this ionization of particular fuel molecules absorption rates of the microwaves by the ignitable mixture in the combustion chamber have to be expected which, however, vary time based over the compression process.
Since the described homogeneity can never be achieved entirely in practical applications the reaction front shall run from an outside in inward direction. Therefore a microwave feed has to be found which generates a field distribution in the circular cylindrical combustion chamber wherein the field distribution increases homogeneously along the entire circumference and increases as homogeneously as possible along a radius or advantageously monotonously increases for larger radii. The homogeneity of the field distribution shall be rendered as independent as possible from absorption properties of the mixture.